Richardson was a partner in the Invercargill, New Zealand firm of Macalister Brothers from 1957 to 1963. From 1963 to 1966, he was Crown Counsel in the Crown Law Office in Wellington. He then joined the Victoria University of Wellington. He was Professor of Law, between 1967 to 1973, during which period he served as Dean of the Law Faculty from 1968 to 1971.
After a period back in public practice in Wellington he was appointed as a judge in the High Court of New Zealand in 1977 and subsequently to the Court of Appeal in the same year. He was invested as a Privy Councillor in 1978. In 2003 he was appointed to the Hong Kong Court of Final Appeal.
He is a Distinguished Fellow at Victoria University.